United Nations observers have begun to leave Syria as their mission officially expires Sunday night at midnight.

At least six of the monitors headed to Beirut, sources told reporters, with the remainder of the 100-member mission set to be gone by August 23.

The mission, which began in April, was extended by one-month intervals several times but was ineffective in stopping or even slowing down the violence against civilians by troops loyal to President Bashar al-Assad.

More than 21,000 civilians have died since the revolt was ignited in March 2011 by the  “Arab Spring” uprisings that swept the region.

According to an agreement reached last Thursday at a meeting of the U.N. Security Council, a token force of seven military observers and five civilian monitors will remain.

The group will staff a new political office to be established in Damascus under the auspices of the U.N. Supervision Mission to Syria (UNSMIS).

Also on Thursday, Algerian diplomat Lakhdar Brahimi was appointed to replace Kofi Annan as the U.N.’s new envoy to the civil war-torn nation.

Annan tendered his resignation earlier in the month in frustration over the ongoing violence resulting in thousands of civilian deaths.